In normal adults, the secretory function of the gonads is stimulated by the pituitary gonadotropins, LH and FSH. The gonadal steroids, in turn, modify secretion of LH and FSH through a feedback loop. During childhood, pituitary LH and FSH secretion is relatively low; gonadal secretions are low, and the hypothalamus, the principal regulator of the system, has a high "set-point" of responsiveness to gonadal steroids. As a result, the hypothalamic-pituitary-gonadal axis is in a relatively quiescent state. With the onset of puberty the hypothalamic "set-point" becomes more sensitive to the stimulatory and maturational effects of gonadal steroids; the production of LH and FSH increases; and in turn, the secretion of gonadal hormones increases. Secretion of the pituitary gonadotropins, LH and FSH, are modulated not only by sex steroids, but also by a gonadal protein, inhibin. Inhibin is a glycoprotein having a molecular weight of approximately 32,000 daltons in the human. It is secreted by testicular sertoli cells and ovarian granulosa cells. The literature contains only a single report of serum concentrations of inhibin during puberty. This report details the results of a cross-sectional study done on single blood samples collected from 99 boys and 102 girls of pubertal ages. We are studying how the gonadotropins, inhibin, and the sex steroids interplay during the normal pubertal process and in children with abnormal puberty by serially measuring plasma levels of these hormones over a 10 hour period and in response to stimulation with luteinizing hormone releasing hormone. In addition, we are studying how the bioactivity of the gonadotropins change in children with central precocious puberty after treatment with a long acting LHRH agonist. We hope that these studies will allow us to better understand how environmental factors such as environmental estrogens can affect the interplay of hormones during the pubertal process.